Floating drilling platform



Dec. 29, 1964 B. G. COLLIPP 3, 7

FLOATING DRILLING PLATFORM Filed May 22, 1961 6 Sheets-Sheet 1 INVENTORLB. G. COLLIPP HIS AGENT Dec. 29, 1964 B. G. COLLIPP 3,163,147

FLOATING DRILLING PLATFORM Filed May 22, 1961 6 Sheets-Sheet 2 INVENTORIB. e. COLLIPP HIS AGENT Dec. 29, 1964 B. G. COLLIPP 3,163,147

FLOATING DRILLING PLATFORM Filed May 22, 1961 6 Sheets-Sheet 5 INVENTORIB. G. COLLlPP IS AGEJNT Dec. 29, 1964 B. G. COLLIPP FLOATING DRILLINGPLATFORM 6 Sheets-Sheet 4 Filed May 22, 1961 FIG. 4A

INVENTORI B. G. COLLIPP BYI H M IS AGENT Dec. 29, 1964 B. e. COLLIPP 3,

FLOATING DRILLING PLATFORM Filed May 22, 1961 6 Sheets-Sheet 5 INVENTORIB. G. COLLIPP BYI .1m

HIS AGENT Dec. 29, 1964 B. G. COLLlPP 3,163,147

FLOATING DRILLING PLATFQRM Filed May 22. 1961 6 SheetsSheet 6 INVENTORIB. G. COLLIPP BY: +7. 9 (l -22g HIS AGENT United States Patent 3,163,147FLOATTNG DRILLHNG PLATFGRM Bruce G. Coliipp, Metairie, La, assignor toShell Gil Company, New York, Nfil, a corporation of Delaware Filed May22, 1961, Ser. No. 111,347 Claims. ((11. 114.5)

This invention relates to apparatus for use in drilling offshore wellsand pertains more particularly to a floating drilling platform which maybe anchored in deep water and from which an underwater well may bedrilled.

In an attempt to locate new oil fields, an increasing amount of welldrilling has been conducted at offshore locations, such for example, asoff the coasts of Louisiana, Texas and California. Well drillingoperations are being carried out further and further from shore and inincreasingly deeper water. At present, however, substantially alloffshore well drilling is being conducted from a platform having legsaffixed to the ocean floor, as by piling, or from mobile drillingplatforms or barges having legs which may be extended downwardly throughthe water and in contact with the ocean floor in order to fixedlysupport the barge thereon. To date, using either of the twoabove-described platforms, well drilling operations have been limited towater depths of about 125 feet. The only known deep Water drilling thathas been conducted to date has taken place from a converted boat inwhich a drilling well has been provided. Since boats are prone to rollfairly easily, deep water drilling operations carried out from boats canonly take place when wind and wave forces are fairly small.

It is therefore an object of the present invention to provide a mooredfloating drilling platform for use in carrying out drilling operationsin waters that are too deep to have bottom supporting legs extendingdown through the water to the ocean floor and to drill during seaconditions not possible with converted boats or too severe for convertedboats.

Another object of the present invention is to provide a floatingdrilling platform having sufficient stability to remain upright inhurricane weather without the assistance of any mooring line forces.

A further object of the present invention is to provide a floatingdrilling platform of the semi-submersible type (one relying on freeboardfor stability, but having much ofits mass underwater) from whichdrilling operations may be carried out economically and safely in deepwaters.

Another object of the present invention is to provide a floatingdrilling platform which is designed with a natural period of movementdifferent from the wave periods so that resonance is avoided.

Still another object of the present invention is to provide a floatingdrilling platform designed to have a natural period of roll larger thanthat of the wave periods to be encountered.

A further object of the present invention is to provide a floatingdrilling platform having stabilizing columns of a design whereby thewave force of the larger waves with heights in excess of a predeterminedheight, say feet, are decreased.

A- further object of the present invention is to provide a floatingdrilling platform having a discontinuous natural period of roll, so thatwhen the vessel rolls more than, say 5 degrees, which occurs only inextremely high waves, means are provided for changing the natural periodof roll from, say, 17 to 32 seconds, thus destroying any resonanceeffect between the waves and the platform.

It is also an object of the present invention to provide a hull ofunique desgn for the floating drilling vessel so forces.

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Still another object of the present invention is to provide a floatingdrilling platform having little natural roll thereby precludingsubjecting drill pipe or casing to stresses as it hangs from thedrilling platform.

It is also an object of the present invention to provide time the hullhas sufficient area in the water plane zone watertight bulkheads asshown'in FIGURE}.

to resist large changes in draft of the platform with changes in deckloads.

Still another object of the present invention is to provide a floatingdrilling platform with a hull of a design which is virtually independentof direction of wave approach whereby motions at 90 for head or beamseas would be the same.

It is also an object of this invention to provide afloat-r 'near thewater surface are ballasted so that damages to them will have little orno effect on the seaworthinessof the platform.

These and other objects of this invention will be understood from thefollowing description taken with reference to the drawing, wherein:

FIGURE 1 is a view showing the outboard profile of the floating platformof the present invention;

FIGURE 2 is a plan view of the floating platform of FIGURE 1;

FIGURE 3 is a diagrammatic plan view of the lower portion of the hull ofthe floating platform of FIG- URE l; v

FEGURE 4 is a schematic view illustrating the ballast system piping inone of the stabilizing legs of the hull;

FIGURE 4A is a plan view of the piping system for flooding andevacuating the buoyancy chambers of the floating platform of the presentinvention;

FIGURE 5 is a diagrammatic view showing the float ing platform beingtowed to a drilling location;

FIGURE 6 is a diagrammatic view showing the floating barge of FIGURE 5after it has been anchored at the drilling location;

FIGURE 7 is a diagrammatic view illustrating the present floatingplatform in its semi-submerged position employed during'drillingoperations;

FIGURE 8 is a diagrammatic View illustrating a tug positioning a bargewith drilling equipment thereon underneath the operating deck of thefloating platform, and

FIGURE 9 is an isometric view of the platform of the present inventionwhen employed as a fluid handling station connected to several wells.

Referring to FlGURE 1 of the drawing, the hull of the floating drillingplatform comprises three vertically-ex tending support or stabilizingcolumns 111, 12 and 13 which are interconnected in a closed triangularconfiguration by cross-bracing hull members 14, 15 and 16 which extendlaterally between the stabilizing columns near the lower ends thereof.The cross-bracing hull members 14, 15 and 16 are preferably hollow,fluidtight members divided into a plurality of buoyancy tanks by meansof Thus,

hull members 14 may be provided with flu'l'dtight bulkheads 17 and 18,while member 15 is provided with fluidtight bulkheads 21 and 22, andmember 16 is provided with fluidtight bulkheads 2 3 and 24. This divideshull member 14 into buoyancy tanks 25, 26 and 27, hull member 15 intobuoyancy tanks 28, 29 and 3t and hull memit ber '16 into buoyancy tanks31, 32 and 33. The hull members 14, and 16 may be interconnected bysmaller and preferably hollow and fluidtight hull members 36, 37 and 33which may also be sub-divided by suitable bulkheads for containing waterand fuel oil to be used during drilling operations.

The three corner support or stabilizing columns ll, 12 and 13 arepreferably in the form of cylindrical tanks, as illustrated, which maybe selectively flooded in order to lower the entire drilling platform inthe water, thus stabilizing it by lowering its center of gravity. Thestabilizing columns ll, 12. and 13 may be of the same diameterthroughout their height, say for example feet in diameter. However, theupper ends il, 4-2 and 43 of the stabilizing columns ll, 12 and 13 arepreferably reduced in diameter a substantial amount, say to 24 feet, ashort distance above the water line when the floating platform is in itssemi-submerged position as illustrated in FIGURE l. The diameter of thelower part of the stabilizing columns ll, 12. and 13 is large in orderto reduce the amount of immersion which takes place when abnormally highhook loads are imposed on the floating platform through the fall linesand derrick. The upper ends ll, 42 and 53 of the stabilizing columns ll,

-12 and 13 are reduced in size to decrease the wave force of the largerWaves with heights in excess of a predetermined size, say 10 feet.

The reduction in diameter of the upper ends ll, 42 and 43 of the supportcolumns ll, 12 and 13 also provides the floating platform with adiscontinuous ma ural period of roll. When the floating platform rollsmore than a predetermined amount, say past 5, which occurs only inextremely high waves, the corner stabilizing column diameter suddenlychanges from 46 feet to 24 feet and the natural period of roll increasesfrom 17 to 32. seconds. Therefore, if the floating platform weresubjected to hurricane waves of a period of 17 seconds so that aresonance build-up occurs, the sudden increase in the natural period ofroll from 17 to 32 seconds for roll angles above 5 would destroy anyfurther resonant affects. Since the natural period of roll of thefloating platform'is a function of the water plane area of thestabilizing columns, a radical change in the natural period of roll ofthe platform takes place when a wave comes along to dip one supportingcolumn below the surface of the water into the range of reduced diameteron the column. Since the period of the vessel and that of the waves arethen different, resonance is destroyed and the amount of roll of thevmsel immediitely decreases.

The stabilizing columns ll, 12 and 13 serve as the primary ballast tankswith the tanks being filled substantially to the water level 44- Whenthe vessel is positioned as shown in FIGURE 1. Each stabilizing columnis provided with a series of circular steel fenders 45 to protect thesemembers from damage by boats. Since the water level inside thestabilizing columns is nearly the same as that outside, a leak caused bya boat rupturing the wall of the column would not be serious. Since thebuoyancy tanks l4, l5 and 16 are deeply submerged and support the weightof the platform there is little likelihood of their being damaged.Damage to the sta bilizing columns would not atiect the intact buoyancytanks so the. platform would neither sink nor heel. This featureprovides a safer floating platform than can be achieved by convertingships. The smaller diameter upper sections 41, 42 and 43 of thestabilizing columns ll, 12 and 13 are separated by a watertight bulkhead(not shown) which would prohibit further flooding of the stabilizingcolumn in case they'Were damaged.

' The ballast system piping for supplying water to and evacuating thestabilizing columns ll, 12 and 13 is shown in FIGURES 3 and 4A. Ballastpiping to the interconnec'ting hull members M, 15 and T16 is preferablyused only in the event it is desired to submerge the platform to adeeper draft than that used for floating drilling 0perations. This canoccur when it is desired to set the platform on the sea floor in shallowwater to efiect repairs. A pump motor d? is provided at the top of eachcolumn with a drive shaft 23 extending downwardly through the column toa pump 43 positioned in the lower end of the large diameter ballasttank. To the intake of the pump l) are connected conduits all, 52, 53and 54 for evacuating fluid from the respective buoyancy chamber anddischarging it up conduit 55 and out conduit 56. Floodtbrough lines 52,53 and 54 is only used when it is desired to set the platform on the seafloor in shallow water as described above. Flooding of the tanks isaccomplished by gravity of iiow of fluid through intake port 57, checkvalve "5% and thence through conduit till into the lower end of the elast tank of. support column ll. All three support columns ll, 12 and 13are provided with pumps 4%, 4 9a and 4% together with the associatedvalves and conduits for flooding and evacuating all buoyancy chambers inthe hull, as shown in FIGURE 4A.

When the Floating drilling platform of the present invention is in itssemi-submerged state, as illustrated in FIG- URE l, the section of thelarge diameter portion of the stabilizing columns ll, 12 and 13 abovethe water line provide reserve buoyancy to absorb heavy shock loads,increase the stability of the vessel, and afford a sharp change in thenatural period of roll pitch as previously discussed. These tanks arefurther designed to have the correct size for the ballast water requiredto bring the platform down to the predetermined drilling draft, izebeing such that the ballast water inside the tanks will be at or nearthe water level outside the tank.

Extending upwardly from the horizontal buoyancy tanks l-l, l5 16, asshown in FIGURE 1, are a plurality of vertical support legs d2, 63, d4for supporting with or w bout the aid of the stabilizing columns, ansuitable type or" operational platform thereon. The buoyant force intanks 1d, 15 and 16 is designed to equal the weight of the equipment andstructure of the support legs d2, 63, 6d and 65 and the operationalplatform. When floating horizontally no vertical force is transmittedbetween stabilizing columns 12. and buoyancy tanks 14 and. 16 forexample. Thus stabilizing column 12 only exerts a vertical force whenthe platform rolls or lists. In this way a safer platform is achieved.The particular platform illustrated is a multi-deck platform having anoperating deck 6'7, a living deck 68 and a storage deck 6.9, as well asa partial or spider deck 7% suspended between the legs 63 and 6 's andwhich is preferably movable horizontally toward and away from the centerhole of the well 59 extending down through the decks and bull. A derrick72 is positioned over the center of the hull structure on the operatingdeck 67. Suitable hoist means '73 and cable reeling means 74 may beprovided. A crane 75 is also provided for hoisting drill pipe and othersupplies onto the drilling vessel. If desired the operational platformmay be entirely supported on the stabilizing columns.

As shown in PEGURE 2 the vessel is provided with a pair of mooring linesF6 and 77 running from the top of each of the stabilizing columns ll, 12and 13. Anchor winches 78 and 79 are provided for handling the anchorlines 76 and '77 which preferably extend outwardly in line with thesides of the hull. As shown in FIGURE 2 a pipe rack 81 is supported byone support column 13 and the operating platform. A casing rack 82 ismounted on the platform diametrically opposite the pipe rack 81 on theopposite side of a rotary table 8-3. A pipe skidway 84 is also provided.

eferring to FIGURES 5 through 8, in FIGURE 5 a pair of tugs 85 and 36are shown towing the floating drilling vessel of the present inventionto a drilling location where six anchor buoys have been previously set.During this stage all of the ballast tanks in the floating rillingvessel are evacuated. In FIGURE 6 the floating drilling vessel has beencentered over the location and anchor cables have been run to the anchorbuoys 90. In FIGURE 7 the sea suction valves of the stabilizing tankshave been opened and the float chambers flooded to lower the vessel inthe water after which the mooring line cables are tightened to apredetermined tension and the ballast in the tanks is adjusted until thevessel is level. FIGURE 8 illustrates a tug 86 moving a barge 87 intoplace between the supporting legs of the platform and beneath the deckthereof. An underwater wellhead structure 88 is mounted on the barge 87and has been centered below the spider deck 70 after which it will beremoved from the barge by a hoist and later lowered to the ocean floorduring drilling operations.

The triangular-shaped semi-submersible vessel of the present inventionprovides a drilling platform that does not have preferred rolling andpitching directions as waves can be taken from any direction and thevessel reacts about the same. Further, the inertia and drag forces onthe present structure are less than those on other rectangularstructures 'assumingthat the same weight is to be supported. Further,the triangular-shaped hull is inherently stronger than a square or otherrectangular shaped hull. A further advantage of the present triangularshaped vessel is that waves passing over the hull members 14, 15 and 16only hit one at a time and strike them at varying angles. Additionally,the tendency for the structure to roll is less with only three legssupporting it than if a greater number were employed.

In FIGURE 9, a floating platform in accordance with the presentinvention is illustrated as a production platform being connected to aplurality of oil or gas Wells for handling the production fluid from thewells and pumping it to shore or to storage facilities. In thisstructure the interconnecting hull members 1%1, 102 and 103 arepreferably arranged in a manner to provide an opening 104 of a size andshape to permit the lowering of a manifold float 105 therethrough of thetype described in copending patent application, Serial No. 75,709, filedDecember 14, 1960, now Patent No. 3,111,692.

The barge of FIGURE 9 is provided with a Gena-a1 platform 196 supportedon legs 167, 108, 109 and 110. Hoists 111 and/or other equipment foroperating the barge and handling Well production fluid may be mounted onplatform 1%, or on the other platforms 112-117 on the tops of thestabilizing columns. Preferably, the platforms support oil separating,treating and metering apparatus through which well roduction fluid isrun before being pumped to shore. The oil and gas may be receivedthrough flexible flowlines 118 and pumped to shore through flowlines119. Alternatively, the oil from the production fluid may be pumped intosome of the tanks in the columns or cross membersof the hull for storagepurposes, displacing some of the water therefrom.

I claim as my invention:

1. A semi-submersible floating platform for carrying out well operationsat offshore locations when in a floating position, said platformcomprising a hull having a plurality of vertically-extending stabilizingcolumns, rigid cross-bracing hull members laterally extending betweensaid stabilizing iCOIlIII'iHS and interconnecting said hull members in atriangular configuration, operational platform means supported by saidstabilizing columns, each of said hull stabilizing columns at the anglesof said triangular configuration containing floodable buoyancy tankmeans at least in the lower part thereof, pump means and valve means andconduit means carried by said drilling platform and being incommunication between the buoyancy tank means of said stabilizingcolumns and the water outside the hull for selectively flooding saidbuoyancy tank means and pumping water therefrom, said tanks beingflooded an amount suflicient to lower the hull in a body of water to thesemi-submerged position taken during drilling operations, each of saidbuoyancy tank means in the lower part of said stabilizing columns being6 filled substantially to the level of said body of water when the hullis in the semi-submerged floating position.

2. A semi-submersible floating drilling platform for drilling wells atoffshore locations when in a floating position, said platform comprisinga hull having a plurality of vertically-extending stabilizing columns,rigid cross-bracing hull members laterally extending between saidstabilizing columns and interconnecting said hull members at least nearthe lower ends thereof in a closed triangular configuration, operationalplatform means supported by said stabilizing columns, each of said hullstabilizing [columns at the angles of said triangular configurationcontaining floodable buoyancy tank means at least in the lower partthereof, pump means and valve means and conduit means carried by saidhull and being in communication between the buoyancy tank means of saidstabilizing columns and the water outside the hull for selectivelyflooding said buoyancy tank means and pumping water therefrom, saidtanks being flooded an amount suflicient to lower the hull in a body ofwater to the semisubmerged position taken during drilling operations,the lower portion of each stabilizing column at the angles of saidtriangular configuration having a cross-section area substantiallygreater than that of the upper portion, the change in cross-sectionalarea taking place at a point near to but above the water level outsidethe stabilizing column in its semi-submerged floating position.

3. A semi-submersible floating drilling platform for drilling wells atoffshore locations when in a floating position, said platform comprisinga hull having a plurality of vertically-extending stabilizing columns,rigid cross-bracing hull members laterally extending between saidstabilizing columns and interconnecting said hull members at least nearthe lower ends thereof in a closed triangular configuration, a pluralityof vertical legs extending upwardly from said lateral hull members,operational platform means supported at least partially by said verticallegs on the tops thereof, each of said hull stabilizing columns at theangles of said triangular configuration containing floodable buoyancytank means at leastin the lower part thereof, pump means and valve meansand conduit means carried by said hull and being in communicationbetween the buoyancy tank means of said stabilizing columns and thewater outside the hull for selectively flooding said buoyancy tank meansand pumping water therefrom, said tanks being flooded an amountsufiicient to lower the hull in abody of water to the semisubmergedposition taken during drilling operations, the lower portion of eachstabilizing column at the angles of said triangular configuration havinga cross-sectional area substantially greater than that of the upperportion, the change in cross-sectional area taking place at a point nearto but above the Water level outisde the stabilizing column in itssemi-submerged floating position.

4. A semi-submersible floating drilling platform for drilling wells atofishore locations when in a floating position, said platform comprisinga hull having a plurality of vertically-extending stabilizing columns,rigid cross-bracing hull members laterally extending between saidstabilizing columns and interconnecting said hull members at least nearthe lower ends thereof in a closed triangular configuration, a pluralityof vertical legs extending upwardly from said lateral hull members,operational platform means supported at least partially by said verticallegs on the top thereof, each of said hull stabilizing columns at theangles of said triangular configuration containing floodable buoyancytank means 'at least in the lower part thereof, said cross-bracing hullmembers being hollow fluid tight membevs at least a portion of whichform buoyancy tank means which are selectively floodable, pump means andvalve means and conduit means carried by said hull and being incommunication between the buoyancy tank means of said stabilizingcolumns and said cross-bracing hull members and the water outside thehull for selectively flooding said buoyancy tank means and pumping Watertherefrom, said tanks being flooded an amount suflicient to lower thehull in a body of water to the semi-submerged position taken duringdrilling operations, the lower portion of each stabilizing column at theangles of said tniangular configuration having a crosssectional areasubstantially greater than that of the upper portion, the change incross-sectional area taking place at a point near to but above the waterlevel outside the stabilizing Column in its semi-submerged floatingposition.

5. The semi-subrnersible floating drilling platform of claim 1 includinga drill derrick supported on the top of said platform means andsubstantially centrally positinned with respect to said triangular hull,said platform means and said hull being provided with a holetherethrough of a size to accommodate the well pipe used during drillingoperations.

References fit ed by the Examiner UNITED ST TES PATENTS FOREIGN PATENTSG erm any.

FERGUS S. MIDDL TON, Primary Examiner.

15 EACOB L. NACKENOFF, MILTON EUCHLER,

Exam iners.

1. A SEMI-SUBMERSIBLE FLOATING PLATFORM FOR CARRYING OUT WELL OPERATIONSAT OFFSHORE LOCATIONS WHEN IN A FLOATING POSITION, SAID PLATFORMCOMPRISING A HULL HAVING A PLURALITY OF VERTICALLY-EXTENDING STABILIZINGCOLUMNS, RIGID CROSS-BRACING HULL MEMBERS LATERALLY EXTENDING BETWEENSAID STABILIZING COLUMNS AND INTERCONNECTING SAID HULL MEMBERS IN ATRIANGULAR CONFIGURATION, OPERATIONAL PLATFORM MEANS SUPPORTED BY SAIDSTABILIZING COLUMNS, EACH OF SAID HULL STABILIZING COLUMNS AT THE ANGLESOF SAID TRIANGULAR CONFIGURATION CONTAINING FLOODABLE BUOYANCY TANKMEANS AT LEAST IN THE LOWER PART THEREOF, PUMP MEANS AND VALVE MEANS ANDCONDUIT MEANS CARRIED BY SAID DRILLING PLATFORM AND BEING INCOMMUNICATION BETWEEN THE BOUYANCY TANK MEANS OF SAID STABILIZINGCOLUMNS AND THE WATER OUTSIDE THE HULL FOR SELECTIVELY FLOODING SAIDBUOYANCY TANK MEANS AND PUMPING WATER THEREFROM, SAID TANKS BEINGFLOODED AN AMOUNT SUFFICIENT TO LOWER THE HULL IN A BODY OF WATER TO THESEMI-SUBMERGED POSITION TAKEN DURING DRILLING OPERATIONS, EACH OF SAIDBUOYANCY TANK MEANS IN THE LOWER PART OF SAID STABILIZING COLUMNS BEINGFILLED SUBSTANTIALLY TO THE LEVEL OF SAID BODY OF WATER WHEN THE HULL ISIN THE SEMI-SUBMERGED FLOATING POSITION.